Zeolitic catalyst and preparation

ABSTRACT

Preformed coherent microspheres obtained by calcining a spray dried slurry of hydrated kaolin clay at elevated temperature (e.g., 1800* F.) are suspended in an aqueous sodium hydroxide solution together with a small amount of finely divided metakaolin (e.g., kaolin clay calcined at 1350* F.). The suspension is aged and then heated until crystalline sodium faujasite appears in the microspheres and a sodium silicate mother liquor is formed. The crystallized microspheres are ionexchanged to produce a fluid zeolitic cracking catalyst.

United States Patent Haden, Jr. et al. 14 1 *May 16, 1972 [54] ZEOLITICCATALYST AND PREPARATION [56] References Cited [72] Inventors: Walter L.Haden, Jr., Metuchen; Frank J. UNITED STATES PATENTS Dzlerzanowski,Somerset, both of NJ. 3,515,684 6/ 1970 McEvoy ..252/455 AsslgneerEnselhard Minerals & Chemicals p 3,532,459 10 1970 McEvoy et al ..23 112s 3,119,659 6/1964 Taggartet al ..23/112 Notice: The portion of the termof this patent sub- 313381672 8/1967 Baden sequent to Apt 14 1987, hasbeen 3,433,587 3/1969 Haden, Jr. et al.. .....23/1 12 claime 3,492,0891] 1970 Vesely ..23/1 12 Filedi 1 1970 Primary Examiner-C. F. Bees [21APPL 10,005 Attorney-Melvin C. Flint and Inez L. Moselle Related US.Application Data [57] ABSTRACT [63] Continuation-impart of Ser. Nos.738,384, June 20; Preformed coherent microspheres obtained by calcininga1968, Pat. No. 3,506,594, and Ser. No. 810,325, Mar. spray dried slurryof hydrated kaolin clay at elevated tempera- 1969, and N0. p 1969, saidture (e.g., 1800 F.) are suspended in an aqueous sodium is acontinuation-in-part of Ser. No. hydroxide solution together with asmall amount of finely di- 693,400, 1963, and $611 vided metakaolin(e.g., kaolin clay calcined at 1350 F.). The 1964, Pat suspension isaged and then heated until crystalline sodium faujasite appears in themicrospheres and a sodium silicate U-S. Cl mother liquor i formed Thecrystallized microsphe es are 1 -C01b 33/231 1 1M0 ion-exchanged toproduce a fluid zeolitic cracking catalyst. [58] Field of Search..252/455 Z;

23/lll-ll3 7 Claims, No Drawings ZEOLITIC CATALYST AND PREPARATIONRELATED APPLICATIONS This application is a continuation-in-part of thefollowing copending U. S. patent applications of W. L. Haden, Jr. and F.J. Dzierzanowski: Ser. No. 738,384, filed June 20, 1968, now US. Pat.No. 3,506,594; Ser. No. 810,325, filed Mar. 25, 1969, and Ser. No.856,458, filed Sept. 9, 1969. Application Ser. No. 738,384 in turn is acontinuation-in-part of copending application Ser. No. 698,400, filedJan. 17, 1968, now US. Pat. No. 3,503,900 and ofSer. No. 416,925, filedDec. 8, 1964 now US. Pat. No. 3,391,994, issued July 9, I968.

BACKGROUND OF THE INVENTION U. S. patent application Ser. No. 738,384describes a process for making a fluid zeolitic molecular sieve crackingcatalyst from preformed microspheres composed of calcined kaolin clay.The microspheres are obtained by mixing water, raw (hydrated) kaolinclay (or a mixture of hydrated and calcined kaolin clay) to form asprayable slurry. The slurry is spray dried, thereby formingmicrospheres which are calcined at a temperature and for a timesufficient to harden the microspheres and to cause the hydrated clay inthe microspheres to undergo or pass through the characteristic kaolinexotherm after the clay is dehydrated. The calcined clay microspheresare subsequently slurried in an aqueous sodium hydroxide solution toform a suspension. This suspension is aged and thereafter heated athigher temperature under agitation until faujasite crystallizes. Duringthe processing, a substantial proportion of the silica in themicrospheres is extracted from the microspheres, forming a sodiumsilicate mother liquor. After reaction and recrystallization, thecrystallized microspheres are separated from at least a portion of themother liquid and the microspheres are subjected to an ion-exchangereaction to replace exchangeable sodium ions with nonalkali cations suchas ammonium ions. Before or during use, the microspheres are steamed orcalcined in air.

The catalytic properties of catalysts obtained by this method areaffected by the proportion of zeolite in the composition as well as theSiO /Al O ratio of the zeolite. Generally, a high SiO /Al O ratio, e.g.,4/1 or above, is desired. For some applications a small proportion ofzeolite, e.g., 5 percent, may be sufficient. For others, higherproportions of zeolite, for example, up to 70 percent, are desired. Whenemploying the high temperature calcined microspheres as the sole sourceof silica and alumina reactants to produce the zeolite, difficulty maybe experienced in crystallizing a sufficient quantity of faujasitehaving a high SiO /Al O ratio. This is especially true when calcinationtemperatures have been severe or when temperature fluctuates duringcalcination, causing partial over-calcination.

It has been found that such difficulties may be obviated by providingmetakaolin and high temperature calcined kaolin clay in separatemicrospheres, suspending the mixture of microspheres in causticsolution, and then aging and crystallizing faujasite. Reference is madeto copending application Ser. No. 810,325.

THE INVENTION This invention results from the discovery that it isbeneficial to incorporate a small amount of powdered metakaolin withpreformed microspheres composed of the high temperature calcined kaolinclay when carrying out the process described in Ser. No. 738,384.

Briefly stated, in accordance with the present invention, a compositezeolitic molecular sieve catalyst in the form of attrition-resistantmicrospheres is prepared by suspending in aqueous sodium hydroxidesolution a mixture of powdered metakaolin and a larger amount ofcoherent spray dried microspheres composed of calcined kaolin clay whichhas undergone the characteristic kaolin exotherm, the microspheres beingsubstantially free from hydrated kaolin clay. The suspension is aged andthen maintained at elevated temperature while it is agitated untilcrystalline faujasite is present in the microspheres in the suspensionand a sodium silicate mother liquor is formed. The zeolitic microspheresare then separated from at least a portion of the mother liquid andpowdered solids that may be present.

The crystalline microspheres are ion-exchanged to replace sodium ionswith suitable cations, the selection of which is within the skill of theart. Prior to use or during use, the ionexchanged microspheres arethermally activated.

By including powdered metakaolin with the calcined clay microspheres inthe reaction mixture, in accordance with this invention, the attritionresistance of the microspherical crystalline product may be improved toa remarkable extent. Especially when the clay has passed completelythrough the kaolin exotherm during calcination of the microspheres, thepercentage of synthetic crystalline faujasite in the product may beincreased.

From the brief description of the present invention, it is apparent thatthe process features the use of metakaolin in the form of a powder alongwith a different form of calcined clay in the form of microsphericalparticles. Although one of the solid reactants is a powder and the otheris in the form of hard microspheres, the ultimate product is obtained inessentially the same size and form as the microspherical reactant.

By introducing the metakaolin into the reaction mixture in the form of apowder, we avoid difficulties that would be encountered in attempts toprovide hard microspheres, all of which contain a mixture of metakaolinand calcined clay which has undergone the exotherm in suitableproportions. This may be explained by the fact that in order to obtainsufficiently attrition-resistant microspheres by spray drying kaolinclay and calcining the spray dried product to harden the microspheres, asubstantial proportion of the clay material in the feed to the spraydryer must be uncalcined (hydrated) kaolin clay. If all of the claywhich is spray dried to produce the microspheres is hydrated and themicrospheres are calcined under conditions which are suitable for thepreparation of metakaolin, the microspheres will not contain clay whichhas undergone the kaolin exotherm and faujasite will not crystallizewhen the microspheres are reacted in caustic solution. Moreover, themicrospheres will lack the desired hardness. On the other hand, ifcalcination of microspheres consisting of hydrated kaolin clay iscarried out under conditions which would be expected to cause the kaolinto undergo or pass through the exotherm, it will be difiicult orimpossible to control the reaction so that a portion of the calcinedclay in the microspheres remains in the form of metakaolin. Similardifficulties will be experienced if the microspheres are produced byspray drying mixtures of hydrated kaolin clay and calcined clay(s) whensuch mixtures include sufficient hydrated clay to provide the desiredhardness. Obviously, if metakaolin and calcined clay which has undergonethe exotherm are both employed as powders, the crystallized product willnot be obtained in the desired form of microspheres.

DETAILED DESCRIPTION Metakaolin and its preparation are described in U.S. Pat. No. 3,338,672 to Haden et al. Briefly, pure metakaolin is anessentially amorphous, anhydrous form of calcined kaolin clay which hasan empirical formula of approximately Al,O -2SiO It may be obtained bycalcining hydrated kaolin clay at a temperature within the range ofabout 1,000 to 1,500 F., usually about l,350- to 1,400 F. When subjectedto conventional differential thermal analysis (DTA), metakaolin exhibitsthe characteristic kaolin exotherm peak at about l,800 F. However, theDTA pattern of metakaolin does not exhibit the characteristicendothermic peak which is associated with loss of water from crystals ofkaolin clay. Preferably the metakaolin is obtained by calcining hydratedkaolin clay supplied in the form of a minus 325 mesh (Tyler) powder.After calcination, the metakaolin should be pulverized if the dischargeproduct from the calciner is in the form of aggregates. The metakaolinpowder may be present as a mixture with some calcined clay that hasundergone or passed through the kaolin exotherm at about 1,800 F. It isalso within the scope of the invention to employ metakaolin whichcontains some hydrated kaolin clay. Commercial metakaolin pigments,exemplified by the product supplied as Satintone No. 2 may be used.

The metakaolin is preferably obtained from a hydrated (raw) clay that islow in iron.

Representative samples of powdered metakaolin have average particlesizes below microns (equivalent spherical diameter). Typical commercialmetakaolin pigments have average particle diameters within the range of2 to 5 microns.

The starting materials employed in producing the calcined microspheresis a micron-size (powdered) clay material selected from the groupconsisting of hydrated kaolin clay and mixtures of hydrated kaolin clayand calcined kaolin clay. The use of a fine size, low-iron plastichydrated kaolin clay, i.e., a clay containing a substantial quantity ofsubmicron size particles, is preferred. The use of such clay generallycontributes to the provision of catalysts of superiorattrition-resistance. Any powdered calcined clay employed in thepreparation of the microspheres may be obtained by calcining pulverizedhigh purity, low iron kaolin clay at a product temperature within therange of about l,000 to 2,200 F., preferably l,350 F. to 2,000 F.Mixtures of clays calcined at temperatures within these ranges may beemployed. The calcined clay constituent may be amorphous when tested bystandard X-ray diffraction although diffraction maxima characteristic ofcrystalline impurities such as anatase may be present. It is within thescope of the invention to include in the slurry a calcined clay whichhas been calcined under conditions such that an X-ray diffractionpattern of the calcined clay contains peaks characteristic of mullite.

In preparing the microspheres, suggested proportions are from 0 to 100parts by weight powdered calcined kaolin clay (moisture-free basis) to100 parts by weight of powdered hydrated kaolin.

To facilitate spray drying of the slurry to form the desiredmicrospheres, the powdered hydrated clay (or mixture thereof withcalcined clay) is preferably dispersed in water in the presence of asmall amount of a deflocculating agent exemplified by a sodium condensedphosphate salt such as tetrasodium pyrophosphate. A sodium condensedphosphate may be employed in amount within the range of about 0.1 to 0.5percent based on the dry weight of the clay material in the slurry.Other deflocculating agents such as sodium silicate may be used. Byemploying a deflocculating agent, spray drying may be carried out athigher solids levels and harder products are usually obtained. When adeflocculating agent is employed, slurries containing about 55 to 65percent solids may be prepared. Such slurries are preferred to 40 to 50percent slurries which do not contain a deflocculating agent. Generallyspeaking, higher solids slurries may be prepared when all of the clay isin hydrated (uncalcined) condition than when mixtures of hydrated andcalcined kaolin clays are employed. Thus, the use of hydrated kaolinclay as the sole clay material in combination with the use of adeflocculating agent is especially preferred.

Other ingredients such as, for example, combustible fillers, may also bepresent in the slurry.

Several procedures can be followed in mixing the ingredients to form theslurry. One procedure, by way of example, is to dry blend the finelydivided solids, add the water and then incorporate the deflocculatingagent. The components can be mechanically worked together orindividually to produce slurries of desired viscosity characteristics.

Spray dryers with countercurrent, cocurrent or mixed countercurrent andcocurrent flow of slurry and hot air can be employed to produce themicrospheres. The air may be heated electrically or by other indirectmeans. Combustion gases obtained by burning hydrocarbon fuel in air canbe used.

Spray drying results in the evaporation of water from droplets of theslurry and the formation of microspheres. Microspheres about 20 to 150microns in equivalent spherical diameter are desired for most catalyticoperations using fluidized contact masses.

Using a cocurrent dryer, air inlet temperatures to 1,200 P. may be usedwhen the clay feed is charged at a rate sufficient to produce an airoutlet temperature within the range of 250 to 600F. At thesetemperatures, free moisture is removed from the slurry without removingwater of hydration (water of crystallization) from the raw clayingredient. Dehydration of some or all of the raw clay during spraydrying is, however, within the scope of the invention. The spray dryerdischarge may be fractionated to recover microspheres of desiredparticle size.

The microspheres obtained by the spray drying operation are calcined ata temperature and for a time such that the hydrated kaolin clay in themicrospheres undergoes substantially or completely the characteristickaolin clay exothermic reaction at about l,800 F. Generally, acalcination atmosphere of at least l,800 F., preferably in excess of1,850 F., is used. In batch operation it is possible to employ asubstantially constant calcination temperature which may be, forexample, within the range of about l800 to 2 F. In a continuous calcinersuch as for example a rotary calciner with countercurrent flow ofcombustion gases of the type described in U. S. Pat. No. 3,383,438 toAllegrini et al, the gas and product temperatures vary throughout thelength of the calciner. When using such a calciner, air inlettemperatures may vary within the range of 2,000 F to 2,400 F.Corresponding product temperatures may be within the range of aboutl,850 to 2,000 F. The product temperature during calcination may becontrolled to provide a product which provides an X-ray pattern freefrom strong lines (except for the possible presence of lines diagnosticfor clay impurities). It is within the scope of the present invention tocalcine the microspheres under conditions of temperature and timesufficiently severe to produce microspheres which produce an X-raypattern having strong lines diagnostic for mullite. It is presentlybelieved that calcination conditions should not be sufficiently severeto cause the crystallization of a substantial proportion ofcristobalite.

After calcination the microspheres should be cooled and fractionated, ifrequired.

The powdered metakaolin and microspheres are formed into an aqueoussuspension by mixing them with sodium hydroxide solution. Any order ofaddition may be followed when making up the suspension.

The suspension is formulated to include proportions of Na O, SiO A1 0and H 0 which will result in the crystallization of a desired percentageof faujasite zeolitic molecular sieve. In formulating the suspension,the sodium hydroxide solution must be employed in amount which willresult in the formation of a suspension which is sufficiently fluid tobe stirred; this suspension must contain sufficient Na O at an operableconcentration to crystallize the desired faujasite zeolite. Recommendedis the use of suflicient sodium hydroxide solution to provide from about0.3 to 1.1 moles Na O per mole A1 0 in the mixture of powderedmetakaolin and calcined microspheres. Sodium hydroxide solutions ofabout 10 percent to 22 percent concentration (w/w) are recommended.Solutions of 14 to 19 percent concentration are preferred. When theconcentration is too high, there may be insufficient liquid to produce afluid suspension without employing a Na O/Al O molar ratio that isexcessively high and results in a zeolite having an undesirably low SiO/Al O molar ratio. When employing the presently preferred sodiumhydroxide solutions of 14 to 19 percent concentration, the preferredproportion of solution to combined metakaolin and microspheres is suchthat the Na O/AI Q, mole ratio in the reaction suspension is within therange ofO.6 to 0.8/1.

The powdered metakaolin is employed in amount within the range of about2 to 35 percent, based upon the combined weight of the powderedmetakaolin and the calcined microspheres. A low ratio of metakaolin tocalcined kaolin clay that has undergone the exotherm favors thecrystallization of zeolite Y. Zeolite X is obtained as the ratio isincreased. When too much metakaolin is present, the desired crystallineproduct may not be obtained even when the hydrothermal treatment iscarried out for long periods of time, e.g., 48 hours or more. On theother hand, when too little metakaolin is present in the reactionliquid, the quantity of zeolite that crystallizes may be less thandesired. This is especially true if the calcined clay in themicrospheres has passed completely through the kaolin exotherm.Generally, the use of metakaolin in amount within the range of 5 topercent of the combined weight of the solid reactants is recommended.

The microspheres and the finely divided metakaolin undergo an exothermicreaction with the sodium hydroxide solution in which they are suspendedsuspended when the suspension is agitated at least intermittently andmaintained at a temperature within the range of about 65 F. to about 130F. for a time within the range of about 6 to 48 hours. During thereaction, silica is extracted from the solids in the suspension andappears in the mother liquor. The sodium oxide content of the reactionliquid undergoes a decrease. Excellent results have been obtained whenthe suspensions were aged at a temperature of 100 F. for times withinthe range of 12 to 24 hours. Crystallization does not take place duringthis phase of the hydrothermal treatment.

To crystallize the zeolite the temperature of the suspension isincreased to about 150 to 200 F. and maintained under at leastinten'nittent agitation. During the crystallization, means should beprovided to prevent substantial change in water content due to loss ofwater from the system. This may be done, for example, by using a closedreactor, by providing the reactor with a water-cooled condensor tocondense water which evaporates or, when operating in an open reactor,by adding water as it is lost from the reactor by evaporation. It isalso within the scope of the invention to employ an open reactor andcover the aqueous suspension with oil. In this case, the impeller usedto agitate the system should be well below the oil layer in order tomaintain the oil as a distinct upper layer.

Crystallization time varies with the composition of the reaction mixtureand temperature and is usually within the range of 8 to 48 hours at atemperature of about 180 F.

Crystallization should be terminated before an appreciable quantity of azeolite having the X-ray difi'raction pattern of zeolite B forms. Whensuch zeolite forms, the proportion of faujasite in the productdecreases.

Only a portion of the constituents of the calcined microspheres reactsto form the zeolitic molecular sieve and thus a composite of crystallinesieve and an alumina-silica residue is present in the crystallizedmicrospheres. Generally speaking, after crystallization the microspheresshould contain above percent crystalline faujasite-type' zeolite, mostpreferably above percent zeolite. The term faujasite-type zeoliteembraces zeolite X and zeolite Y. Preferably, the high silica form ofsodium Y is crystallized, especially sodium zeolite Y having a SiO /Al Omolar ratio in excess of 4.0. X-ray diffraction techniques that may beused to estimate zeolite quantity, distinguish zeolite X from zeolite Y,and determine the silicato-alumina molar ratios of zeolite Y appear inU. S. Pat. No. 3,391,994. As mentioned, silica is extracted from thecalcined clays during reaction and a sodium silicate mother liquorforms. After crystallization a typical mother liquor analyzes about 14percent (wt.) SiO,, 7 percent Na 0 and 0.5 percent A1 0 After reactionand recrystallization, the microspheres are separated from the motherliquid by suitable means such as decantation. Powdered residue of themetakaolin reactant and the residue of any microspheres which may havebeen disintegrated during aging or crystallization are removed with thesupernatant. The reacted suspension may be passed through screens havingopenings of suitable dimensions to separate powdered residue from thecrystallized microspheres.

tions and on the amount of mother liquor retained with the microspheresafter they are separated from the mother liquor. For example, in onetest the microspheres were separated from mother liquor and then washedwith dilute sodium hydroxide solution to prevent precipitation of silicain the mother liquor. The washed and exchanged microspheres had a Slo/A1 0 of 1.09. When another sample of the microspheres was merely washedwith a small amount of distilled water alter they were separated frommother liquor, the microspheres had a SiO /Al O of 1.25 beforeion-exchange. The SiOJAhO, was 1.23 after the partially washedmicrospheres were ion exchanged with ammonium nitrate solution to a Na Oof 0.83 percent.

After mother liquor is removed, exchangeable sodium ions in themicrospheres are exchanged for more suitable nonalkali metal cationssuch as, for example, ammonium, hydrogen, magnesium, calcium, rare earthmetals or mixtures thereof. The exchanged microspheres are dried andthen activated by air calcination, steaming or both. It is within thescope of the invention to activate the ion-exchanged microspheres in acatalytic cracking unit during use of the catalyst.

EXAMPLE I The following tests were carried out to demonstrate advantagesof including a small amount of powdered metakaolin with calcinedmicrospheres composed of kaolin that had undergone the kaolin exothermwhen the microspheres were calcined.

Calcined spray dried microspheres composed predominantly of kaolin claywhich had undergone the characteristic kaolin exotherm were used in acontrol run without added metakaolin (Test A). In Test B and C powderedmetakaolin was incorporated with such microspheres, in accordance withthe present invention.

The calcined microspheres were prepared as follows from HT clay (a finesize fraction of hydrated Georgia kaolin clay, corresponding to a No. 2paper coating grade). An aqueous slurry of the HT clay was deflocculatedwith tetrasodium pyrophosphate in amount of 0.3 percent based on themoisture-free weight of the clay. The ingredients were thoroughly mixed,producing a fluid deflocculated slip containing 60 percent solids. Theslip was spray dried in a 5 X 5 ft. gas-fired spray dryer using anatomizer wheel speed of 16,760 r.p.m. Air inlet and outlet temperatureswere approximately l,l00 and 450F., respectively. A 10 lb. sample of thespray dried microspheres was screened and a minus 60 mesh (Tyler)fraction was recovered. The screened microspheres were charged to silicatrays which were maintained in a muffle furnace for 2 hours at 1,800 F.The resulting porous calcined microspheres consisted largely of calcinedkaolin clay which had undergone the characteristic exotherm and wereessentially free from metakaolin and hydrated kaolin clay.

in carrying out Test A, 150 gm. of the calcined clay microspheres wasgradually charged to 240 gm. of a 16.7 percent (w/w) sodium hydroxidesolution in a 500 ml. Erlenmeyer flask. The mole proportion of Na O inthe solution to A1 0 in the microspheres was 0.74.

Test B (the process of the present invention) was carried out by adding142.5 gm. of the calcined microspheres to 240 gm. of the 16.7 percentsodium solution in another flask. After addition of the microspheres,7.5 gm. Satintone No. 2," a commercial metakaolin pigment, was graduallycharged to the reactor. The Na O/Al O ratio of the reactants was 0.74 tol.

In Test C, also in accordance with the present invention, the procedureof Tests A and B was followed using gm. microspheres, 15 gm. Satintone02 and 240 gm. of the 16.7 percent caustic solution.

In order to control the temperature of the contents of the flask and tomaintain the microspheres in suspension, the flasks were mounted in anEberbach Water Bath Shaker (table model) provided with means to controlthe temperature of the water in the bath surrounding the flasks. Beforethe caustic solution was charged to a flask, the water bath had beenheated to 100 F. The shaker was in operation before the microspheres andmetakaolin were incorporated into the caustic solution.

After the flasks were charged, as described above, they were sealed withrubber stoppers provided with a thin glass tube vent.

The three flasks were maintained (aged) in the 100 F. water bath for 12hours. The temperature of the water bath was then increased to 180 F.and the flasks were held in the bath for an additional 12 hours tocrystallize the zeolite. The flasks were continuously shaken during theaging (100 F.) and crystallizing (180 F.) treatments.

At the end of this period, the flasks were removed from the shaker anddistilled water was added to the flasks. The mother liquor was decantedand the solids were then filtered on Buchner funnels through nylonfilter cloth.

The filter cakes were washed with distilled water and the zeolitecontent of a sample of the washed product was obtained. The washedmaterial was ion-exchanged with 1N NH NO solution to a Na O content lessthan 1 percent and dried.

All X-ray diffraction patterns were obtained by the procedure and withthe equipment described in U. S. Pat. No. 3,391,994. The percentage ofzeolite Y refers to values obtained from X-ray diffraction data usingcalculations described in said patent.

Samples of the 100/270 mesh fraction of the ion-exchanged microsphereswere then calcined in a muffle furnace at l,550 F. for 4 hours.

Hardness (attrition-resistance) of the microspheres was measured asfollows.

A volume of the heat-treated catalyst (0.661 cc.) and 0.5 gm. of 14/20mesh (U. S. Standard Sieve) silica sand was placed in a 2 cc. vial of aWig-L-Bug grinding mill and the mill was operated for 5 seconds. (TheWig-L-Bug grinding mill is a product of Spex Industries, and isdescribed in Catalog No. 5,000 of that company.) The sample was thenscreened and the percentage of minus 325 mesh material was reported asthe percent weight loss. The test was repeated in 5 second increments onthe plus 325 mesh portions of the remainder of the sample. A plot ofpercent weight loss vs. time was obtained. The slope of the curve at 20percent loss was designated the attrition rate. Commercial fluidzeolitic catalysts considered to have outstanding hardness haveattrition values below 1.5 percent by this procedure.

The bulk density of a sample of the calcined ion-exchanged microsphereswas measured to determine the effect of the addition of powderedmetakaolin.

Results are summarized in Table I.

TABLE I Effect of Using Powdered Metakaolin Reactant on Properties ofFluid Zeolitic Cracking Catalyst Obtained from Preformed Calcined KaolinMicrospheres Bulk density, gmJcc. 0.85 0.90 0.97

The data show that by incorporating metakaolin into the suspension ofpreformed calcined kaolin microspheres in caustic solution thepercentage of zeolite Y was increased. The data show that theattrition-resistance was improved to a noteworthy extent and bulkdensity was also increased.

EXAMPLE II This example describes the outstanding catalytic propertiesof a cracking catalyst prepared by the method of the invention.

A fine size fraction of high purity hydrated Georgia kaolin clay (HT)was formed into a 62.5 percent solids deflocculated aqueous slip byagitating the clay in water in the presence of tetrasodium pyrophosphatein amount of 0.30 percent of the clay weight. The slip was spray driedto produce microspheres, as in Example 1. The microspheres were calcinedin a continuous rotary calciner of the type described in the Allegriniet a1 patent (supra). The air inlet temperature during calcination wasin the range of 2,l50 to 2,2S0 F. After the microspheres had cooled, a2,299 lb. portion was blended with 121 lb. of the metakaolin pigmentused in Example l. The mixture was gradually added to 3,865 lb. of a15.0 percent (w/w) aqueous solution of sodium hydroxide in a 500 gallonreactor. The ingredients were mixed and aged at F. for 12 hours and thenmaintained at about F. for 16 hours. During aging and crystallization,the reactor was covered with a loosely fitting cover. Agitation wasintermittent during aging and crystallization. After the reacted mixturehad cooled, it was centrifuged to remove mother liquor and suspendedfine particles.

The residue from the centrifuge was repulped in water and againcentrifuged. This product contained 26 percent zeolite Y having a Si0/Al. ,O of 4.62. A portion of the residue from the centrifuge wasexchanged batchwise with 2N NH NO to a sodium oxide content of 1.14percent. The exchanged product was water washed and air dried at roomtemperature.

The bulk density of a 200/270 mesh fraction of the sample (after beingcalcined at 1,100 F.) was 0.926 g./cc.

The dried product had an L.O.l. (loss on ignition at 1,800 F.) of 24.74percent and a chemical analysis as follows:

Wt. (V.F. Basis) 2 1. 14 A1203 56.03 sio 40.07 n.0, 0.3a "no 2.29

'V.F. volatile free weight basis, determined by heating material toessentially constant weight at 1800" F.

Hardness by the Wig-L-Bug test was 0.50 percent/sec. A comparison ofthis value with those of commercially available fluid cracking catalystsshows that the catalyst of the invention had outstanding resistance toattrition.

A sample of dried ion-exchanged microspheres was pelletized withSterotex" binder and the pellets were activated by heating at 1,350 F.for 4 hours in an atmosphere of 100 percent steam. Catalytic propertieswere tested by the Cat- D procedure at a liquid hourly space velocity(LHSV) of 3 .0.

To test the thermal stability, a portion of the steamed catalyst wascalcined at l,500 F. for 4 hours in 100 percent steam and then tested bythe Cat-D method. Results are summarmed in Table 11.

TABLE II Catalytic Properties of Zeolitic Cracking Catalyst HeatTreatment (steam) 1350 F./4 hr. 1500 F./4 hr.

Gasoline, Vol. 53.8 61.1 Coke, Wt. 8.62 2.66 Gas, Wt. 30.1 15.2 GasGravity 1.66 1.58 Conversion, Wt. 84.0 68.7

Data in Table II show that the catalyst had outstanding selectivitytowards gasoline, low coking properties and excellent stability towardshigh temperature steam.

We claim:

1. A method for preparing a zeolitic molecular sieve catalyst in theform of attrition-resistant microspheres which comprises forrning asuspension comprising (a) mechanically strong microspheres comprisingcalcined kaolin clay which has undergone the kaolin exotherm, saidmicrospheres being free from hydrated clay, (b) powdered metakaolin and(c) an aqueous solution of sodium hydroxide, aging the suspension,subjecting it to agitation, heating the suspension while under agitationuntil faujasite-type zeolite crystals form in said microspheres and asodium silicate mother liquor is formed, separating microspherescomprising crystalline sodium faujasite zeolite from an aqueous phase ofthe suspension and reducing the sodium content of the microspheres byionexchanging them with nonalkali metal cations.

2. The method of claim 1 wherein said metakaolin is incor porated inamount within the range of 2 percent to 35 percent based on the combinedweight of metakaolin and microspheres.

3. The method of claim 1 wherein said metakaolin is incorporated inamount within the range of 5 percent to 10 percent based on the combinedweight of metakaolin and micro spheres.

4. The method of claim 1 wherein the sodium hydroxide solution has aconcentration within the range of 10 percent to 22 percent.

5. The method of claim 1 wherein the sodium hydroxide solution has aconcentration within the range of 14 percent to 19 percent.

6. The method of claim 5 wherein the sodium hydroxide solution is usedin amount to provide from 0.6 to 0.8 mole Na O per mole Al O in themetakaolin and microspheres.

7. A zeolitic molecular sieve catalyst prepared in accordance with themethod of claim 1.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,563,165 Dated May 16 1972 Walter L. Haden, Jr. and Frank J.Dz'ierzanowski Inventor(s) a It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 5 line 18 in which they are suspended suspended" should read inwhich they are suspended line 68, and recrystallization, should read andcrystallization Column 7 line 1, "15 gm. "Satintone 02" should read 15gm. Satintone No. 2

Signed and sealed this 7th day-of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER ,JR.

ROBERT GOTTSCHALK Attesting Officer- Commissioner of Patents FOPMPO-IOSO (10-69) USCOMM-DC 603764 69 U.S. GOVERNMENT PRINYING OFFICE I9690-355-33-1

2. The method of claim 1 wherein said metakaolin is incorporated inamount within the range of 2 percent to 35 percent based on the combinedweight of metakaolin and microspheres.
 3. The method of claim 1 whereinsaid metakaolin is incorporated in amount within the range of 5 percentto 10 percent based on the combined weight of metakaolin andmicrospheres.
 4. The method of claim 1 wherein the sodium hydroxidesolution has a concentration within the range of 10 percent to 22percent.
 5. The method of claim 1 wherein the sodium hydroxide solutionhas a concentration within the range of 14 percent to 19 percent.
 6. Themethod of claim 5 wherein the sodium hydroxide solution is used inamount to provide from 0.6 to 0.8 mole Na2O per mole Al2O3 in themetakaolin and microspheres.
 7. A zeolitic molecular sieve catalystprepared in accordance with the method of claim 1.